I. Field of the Invention
The present invention relates to implantable pulse generators and, more particularly, implantable pulse generator headers and components of such headers. The present invention also relates to methods for manufacturing headers for implantable pulse generators.
II. Discussion of Related Art
In medical technology an implanted pulse generator (IPG) may be employed for a variety of purposes. An IPG is a battery powered device designed to deliver electrical stimulation to the body. An IPG is typically an integral component of a surgically implanted system, which includes the IPG, one or more leads and an external programmer. Such systems are used, for example, to provide deep brain stimulation, vagus nerve stimulation, heart defibrillation, management of heart rhythms, or treatment of other disorders.
The IPG is typically implanted within a person's body, usually beneath the clavicle. Leads are then routed through the body between the site to be stimulated and the IPG. The leads are then coupled to the header of the IPG to carry signals between the IPG and the treatment site. The IPG can be calibrated using the external programmer by a physician (such as an electrophysiologist, neurologist or cardiologist) or by a nurse or other trained technician to meet the individual patient's needs. The IPG must be replaced periodically upon battery depletion. Battery depletion can occur within three to five years, though battery life is dependent on individual usage. End of battery life can be reasonably predicted by the use of a telemetry between the IPG and the external programming device. This allows the IPG to be replaced prior to battery failure.
One example of an IPG is a heart pacemaker (or artificial heart pacemaker, so as not to be confused with the heart's natural pacemaker), a medical device which uses electrical impulses to regulate the beating of the heart. When the IPG is employed as an artificial heart pacemaker, the IPG is used in combination with a lead comprising a set of electrodes which carry stimulation pulses from the IPG to the heart and electrical signals back from the heart to the IPG which senses and responds to such signals. The primary purpose of a pacemaker is to maintain an adequate heart rate, either because the heart's native pacemaker is not fast enough, or because there is a block in the heart's electrical conduction system. Modern pacemakers are externally programmable and allow the electrophysiologist to select the optimum pacing modes for individual patients. Some IPG devices combine a pacemaker and defibrillator in a single implantable device. Multiple electrodes stimulating differing positions within the heart are often used to improve synchronization of the contractions of the upper and lower and chambers of the heart.
Another type of IPG is an implantable cardioverter-defibrillator (ICD), a small battery-powered electrical pulse generator which is implanted in patients who are at risk of sudden death due to ventricular fibrillation or ventricular tachycardia. The device is programmed to detect cardiac arrhythmia and correct it by delivering a jolt of electricity. In current variants, ICD devices have the ability to treat both atrial and ventricular arrhythmias as well as the ability to perform biventricular pacing in patients with congestive heart failure or bradycardia.
The process of implantation of an ICD is similar to implantation of a pacemaker. Like pacemakers, ICD devices are coupled to a set of leads containing electrode(s) and wire(s) which are passed though the vasculature to desired locations in the heart. For example an electrode can be passed through a vein to the right chambers of the heart, and then lodged in the apex of the right ventricle. Providing defibrillation pulses at this location has been found to be advantageous. As is the case with pacemaker leads, the leads are coupled to the header of the ICD and used to carry both stimulation pulses from the ICD to the heart and electrical signals from the heart to the ICD.
ICDs constantly monitor the rate and rhythm of the heart and can deliver therapies, by way of an electrical shock, when the electrical manifestations of the heart activity exceed one or more preset thresholds. More modern devices can distinguish between ventricular fibrillation and ventricular tachycardia (VT) and may try to pace the heart faster than its intrinsic rate in the case of VT, to try to break the tachycardia before it progresses to ventricular fibrillation. This is known as fast-pacing, overdrive pacing or anti-tachycardia pacing (ATP). ATP is only effective if the underlying rhythm is ventricular tachycardia, and is never effective if the rhythm is ventricular fibrillation.
Other IPG devices served as neurostimulators used to treat pain, incontinence, and other neurologic and muscular conditions. Such IPG devices have a header used to couple the IPG to leads containing a plurality of wires and electrodes which deliver stimulating pulses from the IPG to nerves and muscles to provide beneficial therapies. The electrodes and wires of the leads may also be used to carry electrical signals back to the IPG.
The various types of IPG devices referenced above typically have a header to which the leads are attached. The header typically includes one or more bores each configured to receive a terminal pin of a lead. The terminal pin will typically contain a plurality of electrodes spaced along its length. Likewise, the bore will typically have a matching set of electrical contacts along its length which are spaced to form electrical connections with the electrodes of the lead pin. The electrical connections should be isolated from each other to prevent a short or unintended propagation of signals along a particular channel. The number and spacing or the electrodes and contacts may vary, but standards have emerged related to such numbers and such spacing for various types of stimulation systems.
Previous header designs and manufacturing techniques have resulted in difficulty in maintaining component alignment, spacing, and isolation. Likewise, previous header designs and manufacturing techniques made it difficult, if not impossible, to adequately test the assembly before it was fully complete. If testing demonstrates an issue exists with the header after manufacturing is complete, the entire header needs to be discarded and typically none of the components can be salvaged. Thus, to date there has been a real need in the art for a custom solution allowing for interim testing of the electrical components of a bore of a header and the assembly thereof before overmolding of the components is performed to complete the manufacture of the header. More specifically, there is a real need for product design and manufacturing methods which allow conformance to be assessed prior to final part generation, increasing assurance the product meets performance requirements while at the same time decreasing the risk of needing to scrap a more expensive finished product.
The inventors also believe previous devices and manufacturing methods create difficulty in maintaining the desired balance between mechanical and electrical properties. Examples of deficiencies include: (1) a strong mechanical insertion force resulting in excessive pressure exerted on the inner seal and electrical components of the bore; (2) excessive electrical contact resulting in shorts or faults which can draw off potential battery power; (3) insufficient retention forces resulting in an electrode of the bore losing position or falling out of place; and (4) manufacturing tolerances which create challenges related to meeting the electrical and mechanical conformance requirements. The tolerances of the electrode lead wires present further challenges with respect to the header's ability to achieve the desired electrical and mechanical responses. There exists a real and substantial need to provide efficient and cost effective manufacturing methods and designs which meet these challenges.
Prior art header designs often comprise various thin wire connections. Notable are those composed a of spring-type connector in the form of a female leaf spring, canted coil spring or wire “slide by” connector. The inventors believe these devices offer an adequate electrical connection, but are fragile in design. Such connectors can be damaged or broken easily upon insertion of lead pins into the bore. In addition, current designs are expensive to manufacture requiring multiple component pieces and challenging assembly steps driving up cost.
Prior art header designs also provide seals which are intended to isolate the electrical channels, but are subject to failure either during manufacture or as a result of the insertion or removal of lead pins. These seals can also result in alignment problems which arise during overmolding, typically one of the last steps in the manufacturing process. If during overmolding the molding pressures or temperatures deform the seals in an unintended manner, improper alignment of the components and improper sealing can occur. To avoid such problems, thermoset rather than thermoplastic materials requiring lower molding pressure, but longer molding cycle times have often been employed. While the resulting header will work, the header is expensive and time consuming to manufacture. Also, whatever materials and molding techniques are used, great care must be taken to ensure proper alignment and isolation increasing the level of skill and care required to manufacture the header.
For the reasons set forth above, assembly of IPG devices is currently very labor-intensive and time-consuming, and requires skilled craftsmanship on the part of each person performing the assembly steps. In prior assembly methods, each individual component of the bore of the header is individually placed and aligned, either by press fitting and/or fixturing, in a cavity block which is either pre-molded or yet to be cast. Problems associated with these techniques include: electrical leakage between components, electrical failures and excessive force required for inserting and withdrawing lead pins. Such manufacturing techniques result in a high scrap rate and a high scrap cost, since failures are detected only after completion of whole device assembly. Furthermore the final assembly is confined to a specific outer casting design.